1. Field of the Invention
This invention relates to a control system for hybrid vehicles having an internal combustion engine and a traction motor as prime movers.
2. Prior Art
Conventionally, a hybrid vehicle having an internal combustion engine (hereinafter simply referred to as "the engine") and a traction motor as prime movers is widely known, and a control system for controlling the prime movers of such a hybrid vehicle has already been proposed, e.g. by Japanese Laid-Open Patent Publication (Kokai) No. 5-229351.
The proposed control system determines the optimum torque at which the maximum engine efficiency is attained, in dependence on traveling conditions of the vehicle, and at the same time detects actual torque generated by the engine for actually driving the vehicle. Then, the control system determines or selects demanded or required torque from the optimum torque and the actual torque. When the optimum torque is selected as the demanded torque, and at the same time, the optimum torque is larger than the actual torque, regenerative current is caused to be generated for regeneration of energy (specifically, electrical energy).
When the regeneration of energy is carried out by the traction motor, generally the amount of regenerative energy becomes larger with an increase in the rotational speed of the traction motor. On the other hand, as the rotational speed of the motor, i.e. the rotational speed of the engine increases, the loss of energy due to engine braking increases. In addition, the traction motor has a limited capacity with respects to generating electric power, and accordingly it cannot regenerate electrical energy beyond the limit in spite of its increased motor rotational speed.
The conventional control system, however, does not contemplate the relationship between the motor rotational speed, engine braking, and the generating capacity of the motor, and therefore still remains to be improved in terms of efficient collection of kinetic energy of the vehicle as electrical energy.